TP63 is a transcription factor required for the normal development and homeostasis of the skin. Missense mutations in the TP63 gene are linked to a subset of severe developmental disorders, termed ectodermal dysplasias. Our application focuses on two of these, ankyloblepharon ectodermal dysplasia and clefting (AEC) and ectrodactyly ectodermal dysplasia and clefting (EEC), as they are each associated with severe skin erosions. Although EEC has historically not been associated with skin abnormalities, they do occur in a subset of patients (we refer to these patients as EEC/S patients). It is currently not clear how TP63-AEC or TP63-EEC/S mutations lead to the observed skin defects, specifically abnormalities in keratinocyte differentiation, cell- cell adhesion, and cell-extracellular matrix adhesion. While a few deregulated genes associated with AEC have been described, essentially nothing is known regarding the disease mechanism underlying EEC/S. The main goal of this application is to elucidate the cellular and molecular defects underlying AEC and EEC/S and to expand our understanding of the role of TP63 in normal keratinocyte biology. Based on our preliminary data, we hypothesize that desmosomal adhesion and hemidesmosomal adhesion are impaired in AEC and EEC/S patient skin, leading to the observed skin fragility. Further, our results suggest that impaired desmosomal signaling contributes to epidermal differentiation defects in patient skin. The current proposal will establish mechanistic insights into the molecular pathology underlying skin fragility in TP63-related ectodermal dypslasias. Further, we will gain new insights into the epidermal function of TP63, which will broaden our understanding of skin biology in general.